This invention relates to a machine for smoothing and/or polishing a non-spherical curved face of a lens, which face has a different curvature of different angular positions about an optical axis of the lens. Such a face is referred to herein and in the art as a "cylindrical" face but it will be understood that the term embraces forms which cannot be generated by the rotation about an axis of a straight line which is parallel to that axis.
To smooth and polish a cylindrical lens face, the face is rubbed on a layer of an abrasive on a complementary face of a tool. Relative movement of respective reference axes of the lens and tool must be controlled to avoid changing the curvature of the face of the lens and the relative movement must change throughout the operation to avoid the formation of marks on the face of the lens.
Known machines for smoothing and polishing cylindrical faces of lenses have complex driving means for moving one of the tool and the lens relative to the other in a manner such that the locus of a point on the lens relative to a point on the tool shows little regularity. These known driving arrangements cause abrupt changes of direction of the tool or lens and elements of the driving means undergo rapid changes in velocity. These elements must be robust and accordingly are fairly massive.
During operation, the known machines are subjected to severe vibration which is accompanied by excessive noise and by deterioration of the machine. The inertia of moving parts results in variations between the pressure under which the tool contacts the lens at different places on the face of the lens and these variations in pressure result in changes in the curvature of the lens face. A further disadvantage of the known machines is that the driving means is not capable of controlling relative movement of the reference axes of the tool and lens sufficiently accurately. Inaccuracy in such control also leads to changes in the curvature of the lens face.